Page 164 - July-August 2020

dimensional chart. The test relies
on colour dissociation using red/ MADDOX ROD IS A
green complementary filters. This HANDHELD CLINICAL
maximises the ocular deviation. A red ORTHOPTIC INSTRUMENT
WHICH CONSISTS OF
target is illuminated or projected at A GROUP OF RED
the juncture where each tangent line CYLINDRICAL RODS THAT
crosses. A green light is projected by CONVERTS A WHITE
the patient and each plot is recorded. POINT SOURCE OF LIGHT
The test is repeated for the opposite INTO A RED LINE THAT
eye resulting in a chart showing IS PERPENDICULAR
an inner and outer range of ocular TO ITS AXES
rotation for each eye.
LEES SCREEN each other. The screen is used to
obtain the same information about
This apparatus is also based on incomitant strabismus but by using
the principle of providing dissociation a different method of dissociation.
but does not utilise coloured filters The mirror prevents both the eyes
for the purpose. This instrument from viewing the same screen
is essentially a twin-screen where simultaneously, although the patient
the two screens are placed rigidly perceives both images seen by projected straight ahead.
and permanently at right angles to the fovea of each eye as if they are VISUOSCOPE

This instrument is used to detect
amblyopia with eccentric fixation.
The Visuoscope is a type modified
ophthalmoscope that is provided
with a disc which can be brought in
front of the lighting so that a star can
be focused on the retina. The patient
is asked to fix the projected star.

MADDOX PRISM VERGER

This is an excellent instrument
which estimates the vergence power
by rotating the prisms.

Extraocular muscle function
testing examines the function of
the eye muscles. A health care
provider observes the movement
of the eyes in six specific directions.
Some specific instruments are
specially designed for eye muscle
balance. These instruments are
capable of providing the type,
amount and angle of squint which
certainly helps in diagnosing and
managing the case.

| JULY-AUG 2020 | 160 OPTOMETRY